1. Field of the Invention
The present invention relates, in general, to a method of preparing mono-alkyl acid phosphates and, particularly, concerns an improved method of preparing said phosphates with a high mono-content.
2. The Prior Art
Mono-alkyl acid phosphates are well-known, and are generally prepared by reacting alcohols with phosphorus pentoxide. The nature of the chemical reaction between alcohols and phosphorus pentoxide is very nondiscreet. The result, therefore, is a mixture of products including mono-alkyl acid phosphate, di-alkyl acid phosphate, free phosphoric acid, variously substituted pyrophosphate, and, possibly even triphosphate. The situation is further complicated in the case wherein stearyl alcohol is used as it is a solid at room temperature and relatively unreactive. Phosphorus pentoxide is also a solid. Therefore, the reaction between stearyl alcohol and phosphorus pentoxide must be run at a temperature above the melting point of stearyl alcohol (mp 58.degree. C.).
It is particularly advantageous to obtain a product according to the present invention that is high in mono-content. The high mono-content product is more effective than low mono-content products as a surfactant and as an agent for removal of blood stains, egg yolk, and the like from cloth and other materials.
Various methods have been described in the prior art for improving the mono-content in the synthesis of mono-alkyl acid phosphates. In U.S. Pat. No. 2,586,897 for example, water is added to the reaction mixture of lauryl alcohol and phosphorus pentoxide to hydrolyze any acid phosphate esters. This enhances the production of monolauryl phosphate. This technique is also described in U.S. Pat. No. 3,318,982.
It is also known in the prior art to add hydrogen peroxide to the reaction mixture to improve the color of the product.